Photo Credit: Pitchayanan Kongkaew

New findings shed light on optimal pre-surgical myectomy for obstructive HCM imaging techniques and measurement types.

Before patients with obstructive hypertrophic cardiomyopathy (HCM) undergo surgical myectomy, physicians need images and measurements of the mitral valve and septum lengths. Two leading imaging tools are transesophageal echocardiography (TEE) and cardiac magnetic resonance imaging (MRI), though there’s still debate about which is more effective.

Corresponding author Milind Desai, MD, MBA, and colleagues investigated both techniques in a recent study published in the American Journal of Cardiology. Given the results, Dr. Desai tells Physician’s Weekly that “different imaging techniques are not interchangeable, and measurements have to be carefully interpreted after an understanding of nuanced differences.”

Imaging Techniques

Traditionally, surface echocardiography determines a candidate’s eligibility for surgical myectomy. However, physicians often use more advanced multimodality techniques, including TEE and cardiac MRI, for mitral valve and septal measurements, though it is unclear which is more effective.

To test the accuracy of both techniques, Dr. Desai and colleagues recruited 50 patients with obstructive HCM who underwent surgical myectomy in 2018 or 2019. All participants had symptomatic left ventricular (LV) outflow tract obstruction and displayed mitral valve structural abnormalities as a result. The average patient age was 59 ±11 years, and 44% were men.

The study team used 2D and 3D imaging and cardiac MRI to gather measurements for interventricular septum thickness and mitral valve leaflet length.

The settings used for each imaging technique were:

• 2D TEE, performed in mid-esophageal long-axis view. The researchers measured the full posterior mitral length and anterior mitral length in diastole with A2/P2.
• 3D TEE, performed with 3D zoom images, using a mid-esophageal long-axis view in diastole.
• Cardiac MRI, performed with 1.5T and 3T scanners.

Maximum Wall Thickness

The first measurement was the wall thickness of the interventricular septum. Dr. Desai and researchers noted that cardiac MRI is the gold standard for this measurement. The study results confirmed cardiac MRI’s effectiveness, especially in patients with milder degrees of septal hypertrophy.

The three modalities had a moderate correlation of maximum wall thickness. The strongest correlation was between 3D transesophageal echocardiography and cardiac MRI for the distal anteroseptal measurement. However, TEE overestimated wall thickness by an average of 3.9 mm, with overestimations more prominent in 3D TEE than in 2D (Table).

The researchers explained potential reasons why 3D TEE imaging may lead to overestimations, including lower spatial resolution, right ventricular trabeculations, and shadowing due to the inclusion or calcification of crista supraventricular.

Mitral Valve Leaflet Lengths

To capture mitral valve leaflet lengths, the researchers used 2D TEE, zoom 3D TEE with MPR, automatic mitral valve quantification, and cardiac MRI. The researchers measured in a three-chamber view where the leaflet was in mid-diastole and fully elongated.

While cardiac MRI proved effective at measurements related to the interventricular septum, it tended to overestimate the mitral valve leaflet lengths by an average deviation of 0.5 mm (root-mean-square error [RMSE] 17%). In addition, 2D TEE overestimated with an average deviation of 0.6 mm (RMSE 21%). Automatic mitral valve quantification showed no correlation, with a deviation of 0.7 mm (RMSE 24%).

Dr. Desai and team suggested the most accurate modality to capture mitral valve length was the 3D TEE using MPR. However, the researchers added that measurement precision matters significantly when using TEE and could impact imaging accuracy.

There was a modest correlation between 3D TEE and cardiac MRI and between 2D and 3D TEE. However, there was no correlation in posterior leaflet length measurements between the three techniques.

Overall Comparison

Dr. Desai and colleagues concluded that precision is essential regardless of the measurement type or imaging technique.

The authors suggested that different imaging techniques are better suited for different measurements:

• Cardiac MRI: best to determine the wall thickness and left ventricle geometry.
• 3D TEE: best for mitral valve leaflet length measurements. The researchers also noted that intraoperative transesophageal echocardiography is useful for hemodynamic measurements.
• 2D TEE: not recommended as a primary tool for either measurement if the other imaging tools are available.

Performing imaging with correct alignment and recording precise measurements are key, especially when measuring anterior mitral valve length. Precision becomes more important in patients with milder degrees of septal hypertrophy since discrepancies are more evident in this population.

“Cautious interpretation of 3D TEE measurements when making decisions about the extent of basal septal resection during surgical myectomy is needed,” Dr. Desai says. “Bottom line is, there should be detailed preprocedural planning using all available imaging.”